The office of Artur Chilingarov, the bearded polar explorer and anointed Hero of the Russian Federation, is at the end of a long hall in the Duma, Russia's parliament, where he is deputy speaker. Its entrance is guarded by a poster of a nuclear icebreaker, the Yamal, a 492-foot monster with rows of painted-on fangs, and inside is a knee-high wooden penguin and two chicks, a pair of carved walrus tusks, and eight miniature porcelain polar bears—an iconography of the Arctic and Antarctic. On a wall is a portrait of Vladimir Putin. Chilingarov sits in a leather chair in a dark suit with the Hero's gold star pinned to his breast, and next to him sits a four-foot-high globe, normal in every way but one. It has been spun off its axis, reoriented such that both Poles are visible: the Earth turned on its side.

It is winter in Moscow, three months after Chilingarov planted a Russian flag on the seafloor at the North Pole, an apparent landgrab that created a diplomatic row and a flurry of global headlines. Now he is campaigning for an election in which his party—Putin's party—will soon trounce its closest rival by a six-to-one margin. He is a busy man, and he skips the niceties when I sit down. "It took us seven days and seven nights to reach the North Pole," he says. "The ice was heavy. It was not a simple task." Near the Pole, Chilingarov's ships found an opening in the ice, and in went two submersibles, Mir I and Mir II. Chilingarov was in the first one. His goal, the true North Pole, was 14,000 feet below.

"It was dark, very dark," he says of the descent. "Of course it was risky. Of course we were scared." He and fellow parliamentarian Vladimir Gruzdev, a businessman who had paid half a million dollars for his berth, peered out the portholes. Mir II, which had one more paying adventurer, a Swedish businessman, and an Australian tour operator, Mike McDowell, followed. The descent was to take nearly three hours, the return to the surface that long again. Meanwhile, the ice pack would be drifting. If they could not find the opening, they would be stuck. "The depressing thing," Chilingarov tells me, "was knowing no one could come rescue us." Just after midday Mir I touched down on the flat, fine clay of the seabed. The sub scraped up samples of ocean floor, then moved to the Pole itself, where its robotic arm firmly planted a titanium Russian flag in the muck.

"Why did we place it? Well, anytime a country wins something, it installs its flag," he says. Many countries' flags are planted on the surface ice at the North Pole, he points out. At the South Pole there are flags. On top of Mount Everest there are flags. "The Americans even put one on the moon," Chilingarov says. He pulls out a photo of the titanium flag and robotic arm, dramatically signs it with a black marker, and hands it to me. "This is one of the world's greatest geographical achievements," he proclaims. "I'm proud the Russian flag is there." Then he stabs at the photo with his finger, pointing out empty space on the seabed. "Look here, and here, and here, and here," he says. "There is plenty of room for other nations' flags."

Chilingarov mentions that the expedition, widely believed to be an official act of the Kremlin, was privately funded; Putin, far from ordering him to the Pole, had initially cautioned that the dive was too dangerous. A patriot and a politician, well aware his feat made him a national hero, Chilingarov glosses over other little-known details: that the idea originated not with him but with three foreigners—McDowell and two Americans—in 1997, that he joined the team less than a year before the 2007 dive, that McDowell's company had previously been offering a Mir dive to the "real North Pole" to anyone with a spare $95,000, and that the seabed samples they gathered were redundant, of questionable utility to science.

The submersibles' return was harrowing—following Mir I up from the seabed, Mir II searched for an hour and a half before finding the ice opening—but the drama of the dive was soon drowned out by the supposed politics of it. More than 40 journalists were waiting aboard the surface vessels, and they quickly filed their reports: "Russia Claims the North Pole!" Chilingarov willingly stoked nationalist flames. "The Arctic," he said at a press conference, "has always been Russian."

The dive soon became something it had scarcely been: an act of expansionism, not exploration—of geopolitics rather than glorified tourism. Observers seemed ready to believe that the Arctic's future would be decided by flags and warships, belligerence and brinkmanship. Chilingarov's triumph was denounced by Canada, condemned by the Danes, snorted at by the U.S. State Department. Overnight, he became the bearded face of the bitter polar land rush. So one can be forgiven for thinking that this story—the real story of the race for the Arctic—is about Chilingarov. It is not.

This is a story about the changing Arctic,but not only in the ways we expect. The changes most important to its future may be those from millions of years in its past, from times between the Triassic and early Tertiary, when the major basins in the Arctic were just being formed. Pieces of the supercontinent Pangaea were drifting apart, and at times greenhouse gases warmed the world to far hotter than it is today. One might say that parts of the Arctic were, for a time, almost tropical—to some degree because temperatures were higher globally, but more so because parts of the Arctic have not always been in the Arctic: Some drifted north, over geologic time, from warmer latitudes. The creation of oil and gas deposits requires the right mix of organic material, heat, rock, pressure, and passage of time—and it may be hard to look at the Arctic today and imagine that it ever had enough organic life, enough heat. But for geologists, it is hard to imagine that it did not.

Now the floor of the Arctic Ocean appears to be rich in petroleum—home, according to some estimates, to nearly a quarter of the world's undiscovered supply. Sea ice is melting drastically, opening the sea to shipping and the seafloor to mineral exploration. And that seafloor is being eyed by the five countries bordering it—Canada, Denmark (which controls Greenland), Norway, Russia, and the U.S.—all hoping to claim a piece.

On a dreary Thursday exactly two weeks after Chilingarov's flag planting, the oceanographer leading the United States' Arctic effort sits in a Mexican restaurant in Barrow, Alaska, the northernmost town in North America. It is a strange place to be eating chips and salsa, and it is a strange time to be Larry Mayer, a University of New Hampshire professor who is one of the world's few experts in what it takes to claim the ocean floor. Until recently, his task has been obscure; now, thanks to Chilingarov, journalists are calling daily, and foreign governments are watching. Assembled in the restaurant are 21 others—18 scientists, two guys from the State Department, and me—and tomorrow we begin a month-long survey of what may someday become the American Arctic. The&nbsp;Healy, the newest of the U.S. Coast Guard's three aging polar icebreakers, is just offshore, and we will be shuttled to it, three at a time, in a rented helicopter. Before we go, Mayer has a request, one that acknowledges how different things are this year: "No photos of American flags," he says. Everybody laughs. "No, I'm serious," he says. "If a picture gets out in the press, we've got big problems."

For all the talk of conflict in the Arctic, there is broad agreement among northern nations, Russia included, on how to claim a piece of it: You map it. Maps matter because the shape and geology of the seafloor matter, and the shape and geology of the seafloor matter thanks to an article in the 1994 UN Convention on the Law of the Sea, a playbook for partition that has been ratified by 156 countries. (Because of obstructionism by a few UN-wary senators, the U.S. is not yet among them, but it is acting as if it is.) Under the treaty, if a state wants to grow its maritime boundaries past the customary 200 nautical miles, it must prove that the ocean bottom is continental in origin—part of its same landmass, only underwater. Political questions can have scientific answers. So politicians have turned to scientists—oceanographers like Mayer for the seafloor's shape and seismic surveyors for its underlying geology—to build their case. Only Norway has a Law of the Sea submission under active review; the U.S., Canada, Denmark, and Russia are still busy mapping.

Since 2003 Mayer's State Department–directed missions have been charting around the Chukchi Plateau, an undersea ridge that extends nearly 600 miles north of Barrow. His job, he says, is simply to discover what lies beneath the world's least explored ocean; politicians can squabble over what these discoveries mean. The oceanographer's cliché is that we know more about the surface of the moon than about the seafloor, and this is especially true in the Arctic. The first digital chart of the entire Arctic Ocean was released only in 2000, and coverage of the central ocean remains spotty, though it's constantly revised, partly with data from satellites at a thousandth of the resolution of onshore maps. To truly know the seabed's shape, scientists must measure the ocean's depth at various points. Until recently, this higher-resolution data, known as bathymetry, came only from Cold War-era submarine tracks—pencil lines across the polar expanse, often dangerously imprecise. For Mayer, the blanks in the charts are an obsession. If it is nationalism that drives him, rather than pure love of discovery, he hides it well.

For four days and 500 miles, in calm seas mostly free of ice, the Healy cruises north from Barrow to almost 80 degrees. The ship is 4,200 square feet and as stable as solid ground, pervaded by the low hum of its churning engines. I share a stateroom with 26-year-old Barrow native Jimmy Jones Olemaun, an Inupiat observer on board to make sure we do no harm to mammal life. He spends much of his time on the bridge scanning the sea with binoculars, or in the science party's lounge checking his MySpace account. Whenever I leave our room, he turns the thermostat down.

The main lab is near the tail of the ship, just below the waterline and below the empty helicopter hangar where Bronx-born Mayer schools younger scientists on the basketball court. Most researchers have eight-hour lab shifts, but Mayer's is from 9 p.m. to 9 a.m.—and he always seems to be there by day too. He is a workaholic, famous for eating his meals standing up. The son of an air-conditioner technician, he was an A/V monitor during elementary school, got his scuba license in high school, and was a finalist to be a NASA astronaut after graduate school. He has spent five of the past 30 years at sea. Late at night he turns up his Celtic music and taps his loafers to it, and he excitedly flies through 3-D maps of the seafloor, Google Earth–style, in a computer program he helped create. Sometimes rather than return to his stateroom, he naps on the floor.

The hub of mapping activity, usually staffed by a junior scientist, is a jury-rigged wall of 11 screens—two laptops, eight PC monitors, and one closed-circuit TV—that show everything from wind speed to ocean salinity to sediment thickness. The most important monitor has jumpy green lines expanding, contracting, and shifting shape: pings, or sound waves, from the multibeam sonar embedded in the ship's hull. Mayer determines the contours of the seabed by how long it takes them to bounce back. The multibeam covers a 110-degree swath of ocean floor: some 60,000 pings an hour, as many as were available for the entire Arctic before Mayer's effort began. It is a paintbrush rather than a pencil. We watch the Chukchi Plateau rise beneath us on the monitors, the sonar overlaying the charts in real time, as if spraying on a strip of high-resolution data. Currently we are tracing the edge of the Chukchi Plateau, where continental shelf meets deep-ocean plain—the "foot of the slope," a key detail for Law of the Sea claims. In 2003 the multibeam helped Mayer map an unknown 10,000-foot underwater mountain, which he christened Healy Seamount.

While Mayer focuses on bathymetry, other Arctic countries are first gathering seismic data, using air guns or explosives to send out shock waves that penetrate the seabed and reveal its structure. Canada and Denmark have spent millions building a geologic case that the Lomonosov Ridge—the undersea mountain range that bisects the Arctic Ocean, Russia's declared stepladder to the North Pole in a 2001 claim—is in fact connected to their side of the Arctic. (Because America's claim will rely on features that appear not to extend past the 86th parallel, it has no real shot at the Pole. Nor does Norway.) A spring 2006 Canadian-Danish survey of the Lomonosov featured camps on the ice, 970-pound charges under it, and scientists traveling by helicopter to lay out tracks of seismic sensors. In a 2008 follow-up, Canada shipped in 33,000 pounds of explosives and 1,100 pounds of fuel from Montreal on an icebreaker, and then 30 people worked for 30 days in minus 30°F temperatures. In Russia, in a dingy office down a backstreet in St. Petersburg—quarters far less grand than Chilingarov's in the Duma—a geologist leading the country's little-noticed mapping effort showed me a photo of the seismic work on its side of the Lomonosov: men pushing a scary, golf-cart-size mesh sack of dynamite into an ice opening. He was nearly attacked by a mother polar bear and two cubs in the line of mapping duty.

Mayer has his own hurdles: Sonar works poorly in ice, and in a normal year the Healy must limp along at three or four knots to get any data at all. Unfortunately for the Arctic, but fortunately for the mission, this year is far from normal. The enduring mystery of our first week is the location of the ice cap. Our resident ice scientist, Pablo Clemente-Colón, a cigar-smoking Puerto Rican, keeps promising we are about to run into it, wielding satellite reports—official products with names such as AMSR-E, QuikSCAT, and RADARSAT—that show it just hours away. Instead we hit only stray patches of first-year ice—or nothing at all. The ice edge seems to retreat faster than we approach, moving too quickly for the satellites to keep up. We are chasing a ghost.

Already in the 1970s and 1980s, Siberia and Alaska had parallel petroleum booms, but these were mostly on land. Increasingly drillers are looking offshore—and increasingly a former fishing town in Norway, Hammerfest, is a symbol of what may come. When I visit Hammerfest, home to the world's newest and northernmost liquefied natural gas facility, Snøhvit, I expect to see the start of production—but it is a false start, one of many. The gas field is in the Barents Sea, 800 feet underwater, connected by 90 miles of pipes to an ultramodern plant. The plant, on a grassy island abutting the beautiful 9,400-person town, is northern Norway's largest ever industrial project. Viewed from the Hammerfest shopping mall, it is a tangle of smokestacks, lights, and tubes, backed by a fjord and a row of snowy peaks.

For now, StatoilHydro, the operator, will move gas up the pipes, process it, and export it by tanker—half of it to Cove Point, Maryland, half to Bilbao, Spain. But soon carbon dioxide, separated from the natural gas, will travel the other direction down the pipes: StatoilHydro will inject it into the seabed to combat global warming. Snøhvit promises to be one of the world's cleanest petroleum projects. During one test run, however, the winds blew ash from Snøhvit's flares—chimneys burning off excess gas—that turned cars and homes black. StatoilHydro brought in doctors to test for carcinogens and handed out reparations checks to angry residents.

It is a measure of petroleum wealth's appeal that I find only one local politician opposed to the plant: a 19-year-old from the revolutionary-socialist Red party. Snøhvit pays Hammerfest $22 million a year in property taxes. The town is awash in new projects: renovated schools, a bigger airport, a sports arena, a "full-digital," glass-walled cultural center. Strollers are everywhere in the snow-covered streets. It is easy to forget that Hammerfest was recently a dying town, shrinking in population, the most violent place in Norway. In his bay-front office, a local official named Snorre Sundquist is circumspect about Snøhvit. "People didn't like the soot," he says, "but they accepted it."

It is 2 p.m., the Arctic in winter, and it is becoming dark. I step out just in time to see Snøhvit fire up after months of soot-related repairs. A flame spouts hundreds of feet from the tallest chimney, dwarfing the mountains, bathing the town in orange light. From two miles away, I can hear it burn, I can feel the heat on my face.

Whether the future of the Arctic will look like Hammerfest—petroleum plants dotting the coast, an economy running on fossil fuels, and an ice sheet destroyed by them—depends on the world's capacity for irony, and perhaps more on how much oil there really is. In July 2008 the USGS published its "Circum-Arctic Resource Appraisal." It estimated that 13 percent of the world's undiscovered oil, or 90 billion barrels, and 30 percent of its undiscovered natural gas, or 1,670 trillion cubic feet, may be hiding here. But given the unexplored nature of the Arctic, the USGS report is by definition a desktop study: reliant on analogues and best-guess geologic assessments. It uses little of the recent, proprietary seismic work collected by oil companies, settling for older, publicly available data.

Other reports are less rosy, suggesting that the Arctic holds plentiful gas, but far less oil. And in any case, most of the petroleum appears to be near shore—not subject to continental shelf claims because it is within the 200 nautical miles nations already control. The race for the Arctic may be about oil, but it is about the oil that governments hope is there, not the oil they know is there.

The experts best equipped to assess the Arctic's prospects are the oil companies, and a few weeks after my Snøhvit visit, I witness their tacit vote of confidence: a bidding war for nearshore exploration blocks in the Chukchi Sea. The 488 blocks are auctioned off in the Anchorage, Alaska, public library over the protest of environmentalists who want a decision on the polar bear's endangered species status before a sell-off of its habitat. They go for a record $2.66 billion—43 times what the government expected.

There is a second misconception about the race for the Arctic: that it is necessarily a race between nations; if America is to win, Russia must lose. But the market for petroleum is globalized, and so is the hunt, and so are the corporations. The companies vying for projects in Alaska—Shell, StatoilHydro, Chevron, Gazprom, BP, ConocoPhillips—are the same companies vying for projects in Russia and Canada and Norway and Greenland, and their oil is sold on an international market. Where we draw the lines does matter—this will determine who sets the environmental rules and who gets the royalties—but it matters far less than the fact that the lines are being drawn at all. Unless the Arctic countries agree, unless there is legal certainty, companies will not purchase mineral leases, because it won't be clear who can sell them. And the Arctic will remain a wilderness.

It is Saturday, foggy and cold, two weeks into the Healy cruise, when we learn we have broken a record. "It's confirmed," ice scientist Clemente-Colón says, looking up from his computer. "It happened a few days ago." The ice cap has shrunk to its smallest extent in modern history. The ship is now at 77 degrees north, having looped south from a high point above 81 degrees, cutting in and out of the ice sheet, and is scanning the Chukchi Plateau. Clemente-Colón has found occasional pieces of multiyear ice big enough to support a tracking buoy—when out deploying his first one, he cheekily pulled out a tiny Puerto Rican flag—but here most of the ice is patchy, not a solid mass but a series of floes, like asteroid belts. The Healy crashes through. The sun appears, and sailors hit expired survival rations off the helideck with a golf club. They plan a barbecue. A curious feeling, that of being witnesses to a historic moment, washes over the science crew.

In the lab, data stream in unobstructed. We speed up to 10 knots, then 13, then 15. Up on the bridge, my roommate is keeping a tally of seals and polar bears. "Man, last year we were seeing 50 seals a week," Olemaun says. "Now we're lucky if we see one each day." He sees one: "Man, that poor seal." Then reconsiders: "Just imagine if I had my harpoon."

We get reports that the Northwest Passage—the long-sought shipping route across the top of North America, the elusive goal of explorers John Ross, William Edward Parry, John Frank­lin—is ice free for the second year in a row. We learn that the USGS has released a polar bear study: If the melt continues, the world's population—estimated at 22,000 bears—will shrink by two-thirds by 2050. I get an email from someone on one of Shell's seismic ships. His fleet is looking for oil somewhere to our south—he can't say where, but we just passed within 50 miles of each other.

By the time the Healy begins its return, on September 10, the ice cap is the shape of a kidney, just 800 miles across the middle. Olemaun compiles his tally: 17 polar bears, 10 bearded seals, 9 ringed seals, 12 seals of unidentified species, 2 walruses. We learn that walruses are appearing by the dozens on Barrow's beaches: The ice edge, their normal home, is too far away. Locals are distressed, and they are hunting them anyway.

It is a bad summer for ice. It is a bad summer for walruses and polar bears. But it is a good summer for mapping. Before we hit Barrow, the multibeam reveals scours on the seabed 1,300 to 1,600 feet down—likely scrape marks from an ancient ice sheet. Mayer flies around in his map program, giddy, spinning the image of the scours, hovering above them, skimming the seabed at top virtual speed, awestruck by the world he has revealed. The Healy will soon have mapped 6,200 linear miles of seabed in a month—three times what Mayer expected. A NOAA press release will announce the results: Our data suggest that the continental shelf extends more than a hundred miles farther north than previously believed. America is bigger than we thought. Whether it is richer remains to be seen.

The last bear we see is a surprise. It is 2 a.m. at nearly 81 degrees north, and we are in fully open ocean, dozens of miles from the ice pack. Clemente-Colón has decided to place his final buoy into the water—he wants to test if it can transmit when the ice is gone—and most of the crew is awake to watch. Out of the fog, a ten-foot-wide chunk of ice appears—a flash of white, visible for maybe 15 seconds. On it: a polar bear, drifting wherever the ocean wants to take it.